Oxy-cyanoquinolinone PDE9 inhibitors

ABSTRACT

The present invention is directed to oxycyanoquinolinone compounds which may be useful as therapeutic agents for the treatment of central nervous system disorders associated with phosphodiesterase 9 (PDE9). The present invention also relates to the use of such compounds for treating neurological and psychiatric disorders, such as schizophrenia, psychosis or Huntington&#39;s disease, and those associated with striatal hypofunction or basal ganglia dysfunction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. §371 of PCT Application No. PCT/US2016/044167, filed Jul. 27, 2016, whichclaims priority from U.S. Provisional Application No. 62/198,525, filedJul. 29, 2015.

FIELD OF THE INVENTION

The invention relates generally to compounds which act as inhibitors ofthe phosphodiesterase (PDE) 9 enzyme, compositions and therapeutic usesthereof.

BACKGROUND OF THE INVENTION

Schizophrenia is a debilitating disorder affecting the psychic and motorfunctions of the brain. It is typically diagnosed in individuals intheir early to mid-twenties and symptoms include hallucinations anddelusions or at the other extreme, anhedonia or social withdrawal.Across the spectrum, the symptoms are indicative of cognitive impairmentand functional disabilities. Notwithstanding improvements inantipsychotic treatments, current therapies, including typical(haloperidol) and atypical (clozapine or olanzapine) antipsychotics,have been less than acceptable and result in an extremely high rate ofnoncomplicance or discontinuation of medication. Dissatisfaction withtherapy is attributed to lack of efficacy or intolerable andunacceptable side affects. The side effects have been associated withsignificant metabolic, extrapyramidal, prolactic and cardiac adverseevents (Lieberman et al., N. Engl. J. Med. (2005) 353:1209-1223).

While multiple pathways are believed to be involved with thepathogenesis of schizophrenia leading to psychosis and cognitiondeficits, much attention has focused on the role of glutamate/NMDAdysfunction associated with cyclic guanosine monophosphate (cGMP) levelsand the dopaminergic D2 receptor associated with cyclic adenosinemonophosphate (cAMP). These ubiquitous second messengers may beresponsible for altering the function of many intracellular proteins.Cyclic AMP is thought to regulate the activity of cAMP-dependent proteinkinase (PKA), which in turns phosphorylates and regulates many types ofproteins including ion channels, enzymes and transcription factors.Similarly, cGMP may also be responsible for downstream regulation ofkinases and ion channels.

One pathway for affecting the levels of cyclic nucleotides, such as cAMPand cGMP, is to alter or regulate the enzymes that degrade theseenzymes, known as 3′,5′-cyclic nucleotide specific phosphodiesterases(PDEs). The PDE superfamily includes twenty one genes that encode foreleven families of PDEs. These families are further subdivided based oncatalytic domain homology and substrate specificity and include the: (1)cAMP specific, PDE4A-D, 7A and 7B, and 8A and 8B; (2) cGMP specific, PDE5A, 6A-C, and 9A; and (3) those that are dual substrate, PDE 1A-C, 2A,3A and 3B, 10A, and 11A. The homology between the families, ranging from20% to 45% suggests that it may be possible to develop selectiveinhibitors for each of these subtypes.

The identification of PDE9 was recently reported and was distinguishedfrom other PDEs on the basis of its amino acid sequence, functionalproperties, and tissue distribution (Fisher et al., J Biol Chem., 1998,273(25): 15559-64). PDE9V is encoded by two genes (PDE9A and PDE9B) andis cGMP specific. To date, at least 20 different splice variants havebeen discovered (PDE9A1-PD9A20) in human and in mouse (Guipponi et al.,Hum. Genet., 1998, 103(4): 386-92). Structural study of PDE9A have beenshown that its cDNA of the different splice variants share a highpercentage of amino acid identity in the catalytic domain (Rentero etal., Biochem. Biophys. Res. Commun, 2003, 301(3): 686-92). However,despite its highest specificity for cGMP among all the PDEs, PDE9A lacksa GAF domain, whose binding of cGMP usually activates catalyticactivity. Besides its expression in the kidney, spleen, and otherperipheral organs, PDE9 is widespread through the brain in mice, ratsand humans with high similarities of expression in striatum, cerebellum,olfactory bulbs, amygdala and midbrain (van Staveren et al., JNeurocytol 2002, 31(8-9): 729-41). The expression is mainly detected inneurons and astrocytes.

Inhibition of PDE9 is believed to be useful in the treatment ofcognitive deficit associated with neurodegenerative and psychiatricdisorders and a wide variety of conditions or disorders that wouldbenefit from increasing levels of cGMP within neurons, includingAlzheimer's disease, schizophrenia, and depression.

SUMMARY OF THE INVENTION

The present invention is directed to oxycyanoquinolinone compounds whichmay be useful as therapeutic agents for the treatment of central nervoussystem disorders associated with phosphodiesterase 9 (PDE9). The presentinvention also relates to the use of such compounds for treatingneurological and psychiatric disorders, such as schizophrenia, psychosisor Huntington's disease, and those associated with striatal hypofunctionor basal ganglia dysfunction.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compounds of the formula I:

wherein:R⁵ is selected from the group consisting of:

-   -   (1) —C₁₋₆alkyl, which is unsubstituted or substituted with        hydroxy, oxetane, or allyl,    -   (2) -tetrahydropyranyl, and    -   (3) —C₆₋₇cycloalkyl;        or a pharmaceutically acceptable salt thereof.

An embodiment of the present invention includes compounds wherein R⁵ isC₁₋₆alkyl, which is unsubstituted or substituted with hydroxy, oxetane,or allyl.

An embodiment of the present invention includes compounds wherein R⁵ isselected from the group consisting of:

-   -   (1) -tetrahydropyranyl,    -   (2) -cyclohexyl, and    -   (3) -cyclopentyl.

An embodiment of the present invention includes compounds herein, otherthan the compound4-(cyclohexyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile.

Certain embodiments of the present invention include a compound which isselected from the group consisting of the subject compounds of theExamples herein or a pharmaceutically acceptable salt thereof.

The compounds of the present invention may contain one or moreasymmetric centers and can thus occur as racemates and racemic mixtures,single enantiomers, diastereomeric mixtures and individualdiastereomers. Additional asymmetric centers may be present dependingupon the nature of the various substituents on the molecule. Each suchasymmetric center will independently produce two optical isomers and itis intended that all of the possible optical isomers and diastereomersin mixtures and as pure or partially purified compounds are includedwithin the ambit of this invention. The present invention is meant tocomprehend all such isomeric forms of these compounds. Formula I showsthe structure of the class of compounds without specificstereochemistry.

The independent syntheses of these diastereomers or theirchromatographic separations may be achieved as known in the art byappropriate modification of the methodology disclosed herein. Theirabsolute stereochemistry may be determined by the x-ray crystallographyof crystalline products or crystalline intermediates which arederivatized, if necessary, with a reagent containing an asymmetriccenter of known absolute configuration. If desired, racemic mixtures ofthe compounds may be separated so that the individual enantiomers areisolated. The separation can be carried out by methods well known in theart, such as the coupling of a racemic mixture of compounds to anenantiomerically pure compound to form a diastereomeric mixture,followed by separation of the individual diastereomers by standardmethods, such as fractional crystallization or chromatography. Thecoupling reaction is often the formation of salts using anenantiomerically pure acid or base. The diasteromeric derivatives maythen be converted to the pure enantiomers by cleavage of the addedchiral residue. The racemic mixture of the compounds can also beseparated directly by chromatographic methods utilizing chiralstationary phases, which methods are well known in the art.Alternatively, any enantiomer of a compound may be obtained bystereoselective synthesis using optically pure starting materials orreagents of known configuration by methods well known in the art.

The compounds of the present invention may exist in different tautomericforms, and all such forms are embraced within the scope of theinvention. Also, for example, all keto-enol, lactam-lactim andamide-imidic acid forms of the compounds are included in the invention.Thus, for example, the compounds of the invention conforming to theformula:

and their tautomers

are both contemplated as being within the scope of the compounds of theinvention.

As appreciated by those of skill in the art, halogen or halo as usedherein are intended to include fluoro, chloro, bromo and iodo. The termC₁₋₆, as in C₁₋₆alkyl is defined to identify the group as having 1, 2,3, 4, 5 or 6 carbons in a linear or branched arrangement, such thatC₁₋₆alkyl specifically includes methyl, ethyl, n-propyl, iso-propyl,n-butyl, iso-butyl, tert-butyl, pentyl, and hexyl. Substituents (such asR^(1a), R^(1b) and R^(1c)) may be absent if the valency of the group towhich they are attached does not permit such substitution. A group whichis designated as being independently substituted with substituents maybe independently substituted with multiple numbers of such substituents.

The present invention also includes all pharmaceutically acceptableisotopic variations of a compound of the Formula I in which one or moreatoms is replaced by atoms having the same atomic number, but an atomicmass or mass number different from the atomic mass or mass numberusually found in nature. Examples of isotopes suitable for inclusion inthe compounds of the invention include isotopes of hydrogen such as ²Hand ³H, carbon such as ¹¹C, ¹³C and ¹⁴C, nitrogen such as ¹³N and ¹⁵N,oxygen such as ¹⁵O. ¹⁷O and ¹⁸O, phosphorus such as ³²P, sulfur such as³⁵S, fluorine such as ¹⁸F, iodine such as ¹²³I and ¹²⁵I, and chlorinesuch as ³⁶Cl. Certain isotopically-labelled compounds of Formula I, forexample those incorporating a radioactive isotope, are useful in drugand/or substrate tissue distribution studies. The radioactive isotopestritium, i.e. ³H, and carbon-14, i.e. ¹⁴C, are particularly useful forthis purpose in view of their ease of incorporation and ready means ofdetection. Substitution with heavier isotopes such as deuterium, i.e.²H, may afford certain therapeutic advantages resulting from greatermetabolic stability, for example, increased in vivo half-life or reduceddosage requirements, and hence may be preferred in some circumstances.Substitution with positron emitting isotopes, such as ¹¹C, ¹⁸F, ¹⁵O and¹³N, can be useful in Positron Emission Topography (PET) studies forexamining substrate receptor occupancy. An embodiment of the presentinvention includes compounds that are substituted with a positronemitting isotope. An embodiment of the present invention includescompounds that are substituted with a ¹¹C isotope. An embodiment of thepresent invention includes compounds that are substituted with an ¹⁸Fisotope. Isotopically-labelled compounds of Formula I can generally beprepared by conventional techniques known to those skilled in the art orby processes analogous to those described in the accompanying Examplesusing appropriate isotopically-labelled reagents in place of thenon-labelled reagent previously employed.

The term “pharmaceutically acceptable salts” refers to salts preparedfrom pharmaceutically acceptable non-toxic bases or acids includinginorganic or organic bases and inorganic or organic acids. Salts derivedfrom inorganic bases include aluminum, ammonium, calcium, copper,ferric, ferrous, lithium, magnesium, manganic salts, manganous,potassium, sodium, zinc, and the like. Particular embodiments includethe ammonium, calcium, magnesium, potassium, and sodium salts. Salts inthe solid form may exist in more than one crystal structure, and mayalso be in the form of hydrates or solvates. Salts derived frompharmaceutically acceptable organic non-toxic bases include salts ofprimary, secondary, and tertiary amines, substituted amines includingnaturally occurring substituted amines, cyclic amines, and basic ionexchange resins, such as arginine, betaine, caffeine, choline,N,N′-dibenzylethylene-diamine, diethylamine, 2-diethylaminoethanol,2-dimethylaminoethanol, ethanolamine, ethylenediamine,N-ethyl-morpholine, N-ethylpiperidine, glucamine, glucosamine,histidine, hydrabamine, isopropylamine, lysine, methylglucamine,morpholine, piperazine, piperidine, polyamine resins, procaine, purines,theobromine, triethylamine, trimethylamine, tripropylamine,tromethamine, and the like.

When the compound of the present invention is basic, salts may beprepared from pharmaceutically acceptable non-toxic acids, includinginorganic and organic acids. Such acids include acetic, benzenesulfonic,benzoic, camphorsulfonic, citric, ethanesulfonic, fumaric, gluconic,glutamic, hydrobromic, hydrochloric, isethionic, lactic, maleic, malic,mandelic, methanesulfonic, mucic, nitric, pamoic, pantothenic,phosphoric, succinic, sulfuric, tartaric, p-toluenesulfonic acid, andthe like. Particular embodiments include the citric, hydrobromic,hydrochloric, maleic, phosphoric, sulfuric, fumaric, and tartaric acids.It will be understood that, as used herein, references to the compoundsof Formula I are meant to also include the pharmaceutically acceptablesalts.

Exemplifying the invention is the use of the compounds disclosed in theExamples and herein. Specific compounds within the present inventioninclude a compound which is selected from the group consisting of thecompounds disclosed in the following Examples and pharmaceuticallyacceptable salts thereof and individual enantiomers or diastereomersthereof.

The subject compounds may be useful in a method of treating aneurological or psychiatric disorder associated with PDE9 dysfunction ina patient such as a mammal in need of such inhibition comprising theadministration of an effective amount of the compound. In addition toprimates, especially humans, a variety of other mammals may be treatedaccording to the method of the present invention. The subject compoundsmay be useful in a method of inhibiting PDE9 activity in a patient suchas a mammal in need of such inhibition comprising the administration ofan effective amount of the compound. The subject compounds are also maybe useful for treating a neurological or psychiatric disorder associatedwith striatal hypofunction or basal ganglia dysfunction in a mammalianpatient in need thereof. In addition to primates, especially humans, avariety of other mammals may be treated according to the method of thepresent invention.

The present invention is directed to a compound of the present inventionor a pharmaceutically acceptable salt thereof for use in medicine. Thepresent invention is further directed to a use of a compound of thepresent invention or a pharmaceutically acceptable salt thereof for themanufacture of a medicament for treating a neurological or psychiatricdisorder associated with PDE9 dysfunction in a mammalian patient in needthereof. The present invention is further directed to a use of acompound of the present invention or a pharmaceutically acceptable saltthereof for the manufacture of a medicament for treating a neurologicalor psychiatric disorder associated with striatal hypofunction or basalganglia dysfunction in a mammalian patient in need thereof.

“Treating” or “treatment of” a disease state includes: 1) preventing thedisease state, i.e. causing the clinical symptoms of the disease statenot to develop in a subject that may be exposed to or predisposed to thedisease state, but does not yet experience or display symptoms of thedisease state; 2) inhibiting the disease state, i.e., arresting thedevelopment of the disease state or its clinical symptoms; 3) orrelieving the disease state, i.e., causing temporary or permanentregression of the disease state or its clinical symptoms. As usedherein, the terms “treatment” and “treating” refer to all processeswherein there may be a slowing, interrupting, arresting, controlling, orstopping of the progression of the neurological and psychiatricdisorders described herein, but does not necessarily indicate a totalelimination of all disorder symptoms, as well as the prophylactictherapy to retard the progression or reduce the risk of the notedconditions, particularly in a patient who is predisposed to such diseaseor disorder.

The subject treated in the present methods is generally a mammal, inparticular, a human being, male or female, in whom therapy is desired.The term “therapeutically effective amount” means the amount of thesubject compound that will elicit the biological or medical response ofa tissue, system, animal or human that is being sought by theresearcher, veterinarian, medical doctor or other clinician. It isrecognized that one skilled in the art may affect the neurological andpsychiatric disorders by treating a patient presently afflicted with thedisorders or by prophylactically treating a patient afflicted with suchdisorders with an effective amount of the compound of the presentinvention.

Applicants propose that inhibitors of PDE9, and in particular inhibitorsof PDE9A, may provide therapeutic benefit to those individuals sufferingfrom psychiatric and cognitive disorders. The conserved localization ofPDE9 in cortex and hippocampus of rodents and humans, brain regions thatplay a key role in memory and learning, together with the previouslydescribed role for NO/cGMP/PKG signaling in synaptic plasticity andcognition has focused attention on a possible role for PDE9 in cognitivefunction and consequently as a therapeutic target for cognitivedysfunction in Alzheimer's disease and schizophrenia. The mechanism bywhich PDE9 inhibition improve cognitive function through the modulationof glutamate and/or cholinergic neuron signaling is potentially feasiblegiven that both glutamate (NMDA) and cholinergic receptor activationenhance the formation of cGMP in brain and both neural substrates areinvolved in cognitive function.

As used herein, the term “selective PDE9 inhibitor” refers to an organicmolecule that effectively inhibits an enzyme from the PDE9 family to agreater extent than enzymes from the PDE 1-8 or PDE10-11 families. Inone embodiment, a selective PDE9 inhibitor is an organic molecule havinga Ki for inhibition of PDE9 that is less than or about one-tenth thatfor a substance that is an inhibitor for another PDE enzyme. In otherwords, the organic molecule inhibits PDE9 activity to the same degree ata concentration of about one-tenth or less than the concentrationrequired for any other PDE enzyme. Preferably, a selective PDE9inhibitor is an organic molecule, having a Ki for inhibition of PDE9that is less than or about one-hundredth that for a substance that is aninhibitor for another PDE enzyme. In other words, the organic moleculeinhibits PDE9 activity to the same degree at a concentration of aboutone-hundredth or less than the concentration required for any other PDEenzyme. A “selective PDE9 inhibitor” can be identified, for example, bycomparing the ability of an organic molecule to inhibit PDE9 activity toits ability to inhibit PDE enzymes from the other PDE families. Forexample, an organic molecule may be assayed for its ability to inhibitPDE9 activity, as well as PDE1A, PDE1B, PDE1C, PDE2A, PDE3A, PDE3B,PDE4A, PDE4B, PDE4C, PDE4D, PDE5A, PDE6A, PDE6B, PDE6C, PDE7A, PDE7B,PDE8A, PDE8B, PDE10A, and/or PDE11A.

Phosphodiesterase enzymes including PDE9 have been implicated in a widerange of biological functions. This has suggested a potential role forthese enzymes in a variety of disease processes in humans or otherspecies. The compounds of the present invention may have utility intreating a variety of neurological and psychiatric disorders.

In a specific embodiment, compounds of the present invention may providea method for treating schizophrenia or psychosis comprisingadministering to a patient in need thereof an effective amount of acompound of the present invention. The Diagnostic and Statistical Manualof Mental Disorders (DSM-IV-TR) (2000, American Psychiatric Association,Washington D.C.) provides a diagnostic tool that includes paranoid,disorganized, catatonic or undifferentiated schizophrenia andsubstance-induced psychotic disorders. As used herein, the term“schizophrenia or psychosis” includes the diagnosis and classificationof these mental disorders as described in DSM-IV-TR and the term isintended to include similar disorders described in other sources.Disorders and conditions encompassed herein include, but are not limitedto, conditions or diseases such as schizophrenia or psychosis, includingschizophrenia (paranoid, disorganized, catatonic, undifferentiated, orresidual type), schizophreniform disorder, schizoaffective disorder, forexample of the delusional type or the depressive type, delusionaldisorder, psychotic disorder, brief psychotic disorder, shared psychoticdisorder, psychotic disorder due to a general medical condition andsubstance-induced or drug-induced (for example psychosis induced byalcohol, amphetamine, cannabis, cocaine, hallucinogens, inhalants,opioids, phencyclidine, ketamine and other dissociative anaesthetics,and other psychostimulants), psychosispsychotic disorder, psychosisassociated with affective disorders, brief reactive psychosis,schizoaffective psychosis, “schizophrenia-spectrum” disorders such asschizoid or schizotypal personality disorders, personality disorder ofthe paranoid type, personality disorder of the schizoid type, illnessassociated with psychosis (such as major depression, manic depressive(bipolar) disorder, Alzheimer's disease and post-traumatic stresssyndrome), including both the positive and the negative symptoms ofschizophrenia and other psychoses.

In another specific embodiment, the compounds of the present inventionmay provide a method for treating cognitive disorders comprisingadministering to a patient in need thereof an effective amount of acompound of the present invention. The DSM-IV-TR also provides adiagnostic tool that includes cognitive disorders including dementia,delirium, amnestic disorders and age-related cognitive decline. As usedherein, the term “cognitive disorders” includes the diagnosis andclassification of these disorders as described in DSM-IV-TR and the termis intended to include similar disorders described in other sources.Disorders and conditions encompassed herein include, but are not limitedto, disorders that comprise as a symptom a deficiency in attentionand/or cognition, such as dementia (associated with Alzheimer's disease,ischemia, multi-infarct dementia, trauma, intracranial tumors, cerebraltrauma, vascular problems or stroke, alcoholic dementia or otherdrug-related dementia, AIDS, HIV disease, Parkinson's disease,Huntington's disease, Pick's disease, Creutzfeldt Jacob disease,perinatal hypoxia, other general medical conditions or substance abuse),Alzheimer's disease, multi-infarct dementia, AIDS-related dementia, andFronto temperal dementia, delirium, amnestic disorders or age relatedcognitive decline.

In another specific embodiment, compounds of the present invention mayprovide a method for treating anxiety disorders comprising administeringto a patient in need thereof an effective amount of a compound of thepresent invention. The DSM-IV-TR also provides a diagnostic tool thatincludes anxiety disorders as generalized anxiety disorder,obsessive-compulsive disorder and panic attack. As used herein, the term“anxiety disorders” includes the diagnosis and classification of thesemental disorders as described in DSM-IV-TR and the term is intended toinclude similar disorders described in other sources. Disorders andconditions encompassed herein include, but are not limited to, anxietydisorders such as, acute stress disorder, agoraphobia, generalizedanxiety disorder, obsessive-compulsive disorder, panic attack, panicdisorder, post-traumatic stress disorder, separation anxiety disorder,social phobia, specific phobia, substance-induced anxiety disorder andanxiety due to a general medical condition.

In another specific embodiment, compounds of the present invention mayprovide a method for treating substance-related disorders and addictivebehaviors comprising administering to a patient in need thereof aneffective amount of a compound of the present invention. The DSM-IV-TRalso provides a diagnostic tool that includes persisting dementia,persisting amnestic disorder, psychotic disorder or anxiety disorderinduced by substance abuse, and tolerance of, dependence on orwithdrawal from substances of abuse. As used herein, the term“substance-related disorders and addictive behaviors” includes thediagnosis and classification of these mental disorders as described inDSM-IV-TR and the term is intended to include similar disordersdescribed in other sources. Disorders and conditions encompassed hereininclude, but are not limited to, substance-related disorders andaddictive behaviors, such as substance-induced delirium, persistingdementia, persisting amnestic disorder, psychotic disorder or anxietydisorder, drug addiction, tolerance, and dependence or withdrawal fromsubstances including alcohol, amphetamines, cannabis, cocaine,hallucinogens, inhalants, nicotine, opioids, phencyclidine, sedatives,hypnotics or anxiolytics.

In another specific embodiment, compounds of the present invention mayprovide a method for treating obesity or eating disorders associatedwith excessive food intake, and complications associated therewith,comprising administering to a patient in need thereof an effectiveamount of a compound of the present invention. At present, obesity isincluded in the tenth edition of the International Classification ofDiseases and Related Health Problems (ICD-10) (1992 World HealthOrganization) as a general medical condition. The DSM-IV-TR alsoprovides a diagnostic tool that includes obesity in the presence ofpsychological factors affecting medical condition. As used herein, theterm “obesity or eating disorders associated with excessive food intake”includes the diagnosis and classification of these medical conditionsand disorders described in ICD-10 and DSM-IV-TR and the term is intendedto include similar disorders described in other sources. Disorders andconditions encompassed herein include, but are not limited to, obesity,bulimia nervosa and compulsive eating disorders.

In another specific embodiment, compounds of the present invention mayprovide a method for treating mood and depressive disorders comprisingadministering to a patient in need thereof an effective amount of acompound of the present invention. As used herein, the term “mood anddepressive disorders” includes the diagnosis and classification of thesemedical conditions and disorders described in the DSM-IV-TR and the termis intended to include similar disorders described in other sources.Disorders and conditions encompassed herein include, but are not limitedto, bipolar disorders, mood disorders including depressive disorders,major depressive episode of the mild, moderate or severe type, a manicor mixed mood episode, a hypomanic mood episode, a depressive episodewith atypical features, a depressive episode with melancholic features,a depressive episode with catatonic features, a mood episode withpostpartum onset, post-stroke depression; major depressive disorder,dysthymic disorder, minor depressive disorder, premenstrual dysphoricdisorder, post-psychotic depressive disorder of schizophrenia, a majordepressive disorder superimposed on a psychotic disorder such asdelusional disorder or schizophrenia, a bipolar disorder, for example,bipolar I disorder, bipolar II disorder, cyclothymic disorder,depression including unipolar depression, seasonal depression andpost-partum depression, premenstrual syndrome (PMS) and premenstrualdysphoric disorder (PDD), mood disorders due to a general medicalcondition, and substance-induced mood disorders.

In another specific embodiment, compounds of the present invention mayprovide a method for treating pain comprising administering to a patientin need thereof an effective amount of a compound of the presentinvention. Particular pain embodiments are bone and joint pain(osteoarthritis), repetitive motion pain, dental pain, cancer pain,myofascial pain (muscular injury, fibromyalgia), perioperative pain(general surgery, gynecological), chronic pain and neuropathic pain.

In other specific embodiments, compounds of the invention may providemethods for treating other types of cognitive, learning and mentalrelated disorders including, but not limited to, learning disorders,such as a reading disorder, a mathematics disorder, or a disorder ofwritten expression, attention-deficit/hyperactivity disorder,age-related cognitive decline, pervasive developmental disorderincluding autistic disorder, attention disorders such asattention-deficit hyperactivity disorder (ADHD) and conduct disorder; anNMDA receptor-related disorder, such as autism, depression, benignforgetfulness, childhood learning disorders and closed head injury; aneurodegenerative disorder or condition, such as neurodegenerationassociated with cerebral trauma, stroke, cerebral infarct, epilepticseizure, neurotoxin poisoning, or hypoglycemia-inducedneurodegeneration; multi-system atrophy; movement disorders, such asakinesias and akinetic-rigid syndromes (including, Parkinson's disease,drug-induced parkinsonism, post-encephalitic parkinsonism, progressivesupranuclear palsy, multiple system atrophy, corticobasal degeneration,parkinsonism-ALS dementia complex and basal ganglia calcification),medication-induced parkinsonism (such as, neuroleptic-inducedparkinsonism, neuroleptic malignant syndrome, neuroleptic-induced acutedystonia, neuroleptic-induced acute akathisia, neuroleptic-inducedtardive dyskinesia and medication-induced postural tremor), Huntington'sdisease, dyskinesia associated with dopamine agonist therapy, Gilles dela Tourette's syndrome, epilepsy, muscular spasms and disordersassociated with muscular spasticity or weakness including tremors;dyskinesias, including tremor (such as, rest tremor, postural tremor,intention tremor and essential tremor), restless leg syndrome, chorea(such as Sydenham's chorea, Huntington's disease, benign hereditarychorea, neuroacanthocytosis, symptomatic chorea, drug-induced chorea andhemiballism), myoclonus (including, generalised myoclonus and focalmyoclonus), tics (including, simple tics, complex tics and symptomatictics), dystonia (including, generalised, iodiopathic, drug-induced,symptomatic, paroxymal, and focal (such as blepharospasm, oromandibular,spasmodic, spasmodic torticollis, axial dystonia, hemiplegic anddystonic writer's cramp)); urinary incontinence; neuronal damage(including ocular damage, retinopathy or macular degeneration of theeye, tinnitus, hearing impairment and loss, and brain edema); emesis;and sleep disorders, including insomnia and narcolepsy.

Of the disorders above, the treatment of schizophrenia, bipolardisorder, depression, including unipolar depression, seasonal depressionand post-partum depression, premenstrual syndrome (PMS) and premenstrualdysphoric disorder (PDD), learning disorders, pervasive developmentaldisorders, including autistic disorder, attention disorders includingAttention-Deficit/Hyperactivity Disorder, autism, tic disordersincluding Tourette's disorder, anxiety disorders including phobia andpost traumatic stress disorder, cognitive disorders associated withdementia, AIDS dementia, Alzheimer's, Parkinson's, Huntington's disease,spasticity, myoclonus, muscle spasm, tinnitus and hearing impairment andloss are of particular importance.

The activity of the compounds in accordance with the present inventionas PDE9 inhibitors may be readily determined without undueexperimentation using a fluorescence polarization (FP) methodology thatis well known in the art (Huang, W., et al., J. Biomol Screen, 2002, 7:215). In particular, the compounds of the following examples hadactivity in reference assays by exhibiting the ability to inhibit thehydrolysis of the phosphosphate ester bond of a cyclic nucleotide.

In a typical experiment the PDE9 inhibitory activity of the compounds ofthe present invention was determined in accordance with the followingexperimental method. Rhesus PDE9A2 was amplified from rhesus whole braincDNA (Biochain Institute) essentially as described in Hutson, et al.Neuropharmacology (2011) 61(4):665-676. HEK 293 or CHO cellsover-expressing rhesus or rat PDE9A2 (created by DiscoverX from mRNAGenbank accession # NM_138543) respectively were lysed in 20 mM HEPES, 1mM EDTA buffer with protease inhibitors (Roche, Indianapolis, Ind.).After brief homogenization, cells were pelleted via centrifugation at75,000×g for 20 min at 4° C. The pellets were re-suspended, centrifugedand re-pelleted again in the same manner. The membrane fraction wascollected in 20 mM HEPES, 1 mM MgCl2 with protease inhibitors. HumanPDE9 (PDE9A2, GenBank Accession No. NM_001001567), full length withN-terminal GST tag, was purchased from BPS Bioscience. The fluorescencepolarization assay for cyclic nucleotide phosphodiesterases wasperformed using an IMAP® FP kit supplied by Molecular Devices,Sunnyvale, Calif. (product # R8139). IMAP® technology has been appliedpreviously to phosphodiesterase assays (Huang, W., et al., J. BiomolScreen, 2002, 7: 215). Assays were performed at room temperature in384-well microtiter plates with an incubation volume of 20.2 μL.Solutions of test compounds were prepared in DMSO and serially dilutedwith DMSO to yield 8 μL of each of 10 solutions differing by 3-fold inconcentration, at 32 serial dilutions per plate. 100% inhibition isdetermined using a known PDE9 inhibitor, such as1-(2-chlorophenyl)-6-[(2R)-3,3,3-trifluoro-2-methylpropyl]-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidine-4-one(BAY 73-6691) (Wunder et al, Mol. Pharmacol., 2005, 68(6): 1775-81),(6-[(3S,4S)-4-methyl-1-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl]-1-(tetrahydro-2H-pyran-4-yl)-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one(PF-04447943) (Wager et al., ACS Chemical Neuroscience, 2010,1:435-449). 0% of inhibition is determined by using DMSO (1% finalconcentrations). A Labcyte Echo 555 (Labcyte, Sunnyvale, Calif.) is usedto dispense 200 nL from each well of the titration plate to the 384 wellassay plate. Rhesus membrane preps were diluted to 4 ng/ml, rat membranepreps diluted to 13 ng/ml, and human PDE9A2 diluted to 1 ng/ml.FAM-labeled cGMP substrate (Molecular Devices, Sunnyvale, Calif.) was ata concentration of 100 nM (Km of PDE9 for cGMP is 70-170 nM) in theassay buffer (10 mM Tris HCl, pH 7.2, 10 mM MgCl2, 0.05% NaN₃ 0.01%Tween-20, and 1 mM DTT). PDE9 enzyme mix and compounds were mixed andincubated at room temperature for 30 min. Following which, FAMcGMPsubstrate was added, shaken and incubated for an additional 60 min atroom temperature. The final concentrations of rhesus and rat membranepreparations were 2 ng/ml and 6.5 ng/ml, respectively, while the humanPDE9 was used at a final concentration of 0.5 ng/ml. The finalconcentration of FAM-cGMP was 50 nM. After the incubation period, theenzymatic reaction was stopped by addition of binding solution (IMAP-FP,Molecular Devices, comprised of 80% Solution A, 20% Solution B and a1:600 dilution of binding reagent) to each well. The plates were shakenthen incubated at room temperature for 1 h prior to determining thefluorescence polarization (mP) using a Perkin Elmer EnVision™ platereader (Waltham, Mass.).

Fluorescence polarization (mP) was calculated from the parallel (S) andperpendicular (P) fluorescence of each sample well and the analogousvalues for the median control well, containing only substrate (So andPo), using the following equation:Polarization(mP)=1000*(S/So−P/Po)/(S/So+P/Po).

Dose-inhibition profiles for each compound were characterized by fittingthe mP data to a four-parameter equation given below. The apparentinhibition constant (K_(I)), the maximum inhibition at the low plateaurelative to “100% Inhibition Control” (Imax; e.g. 1=>same as thiscontrol), the minimum inhibition at the high plateau relative to the “0%Inhibition Control” (Imin, e.g. 0=>same as the no drug control) and theHill slope (nH) are determined by a non-linear least squares fitting ofthe mP values as a function of dose of the compound using an in-housesoftware based on the procedures described by Mosser et al., JALA, 2003,8: 54-63, using the following equation:

${mP} = {\frac{\left( {{0\%{mP}} - {100\%{mP}}} \right)\left( {{Imax} - {Imin}} \right)}{1 + \left\lbrack \frac{\lbrack{Drug}\rbrack}{\left( {10^{- {pK}_{1}}\left( {1 + \frac{\lbrack{Substrate}\rbrack}{K_{M}}} \right)} \right.} \right\rbrack^{nH}} + {100\%{mP}} + {\left( {{0\%{mP}} - {100\%{mP}}} \right)\left( {1 - {Imax}} \right)}}$

The median signal of the “0% inhibition controls” (0% mP) and the mediansignal of the “100% inhibition controls” (100% mP) are constantsdetermined from the controls located in columns 1-2 and 23-24 of eachassay plate. An apparent (K_(m)) for FAM-labeled cAMP of 150 nM wasdetermined in separate experiments through simultaneous variation ofsubstrate and selected drug concentrations.

Selectivity for PDE9, as compared to other PDE families, was assessedusing the IMAP® technology. Rhesus PDE2A3 and Human PDE10A2 enzyme wasprepared from cytosolic fractions of transiently transfected HEK cells.All other PDE's were GST Tag human enzyme expressed in insect cells andwere obtained from BPS Bioscience (San Diego, Calif.): PDE1A(Cat#60010), PDE3A (Cat#60030), PDE4A1A (Cat#60040), PDE5A1 (Cat#60050),PDE6C (Cat#60060), PDE7A (Cat#60070), PDE8A1 (Cat#60080), PDE9A2(Cat#60090), PDE11A4 (Cat#60110).

Assays for PDE 1 through 11 were performed in parallel at roomtemperature in 384-well microtiter plates with an incubation volume of20.2 μL. Solutions of test compounds were prepared in DMSO and seriallydiluted with DMSO to yield 30 μL of each of ten solutions differing by3-fold in concentration, at 32 serial dilutions per plate. 100%inhibition was determined by adding buffer in place of the enzyme and 0%inhibition is determined by using DMSO (1% final concentrations). ALabcyte POD 810 (Labcyte, Sunnyvale, Calif.) was used to dispense 200 nLfrom each well of the titration plate to make eleven copies of the assayplate for each titration, one copy for each PDE enzyme. A solution ofeach enzyme (dilution from aliquots, sufficient to produce 20% substrateconversion) and a separate solution of FAM-labeled cAMP or FAM-labeledcGMP from Molecular Devices (Sunnyvale, Calif., product # R7506 orcGMP#R7508), at a final concentration of 50 nM were made in the assaybuffer (10 mM Tris HCl, pH 7.2, 10 mM MgCl₂, 0.05% NaN₃ 0.01% Tween-20,and 1 mM DTT). Note that the substrate for PDE2 is 50 nM FAM cAMPcontaining 1000 nM of cGMP. The enzyme and the substrate were then addedto the assay plates in two consecutive additions of 10 μL and thenshaken to mix. The reaction was allowed to proceed at room temperaturefor 60 minutes. A binding solution was then made from the kitcomponents, comprised of 80% Solution A, 20% Solution B and bindingreagent at a volume of 1/600 the total binding solution. The enzymaticreaction was stopped by addition of 60 μL of the binding solution toeach well of the assay plate. The plates were sealed and shaken for 10seconds. The plates were incubated at room temperature for one hour. Theparallel and perpendicular fluorescence of each well of the plate wasmeasured using a Perkin Elmer EnVision™ plate reader (Waltham, Mass.).The apparent inhibition constants for the compounds against all 11 PDE'swas determined from the parallel and perpendicular fluorescent readingsas described for PDE FP assay using the following apparent K_(M) valuesfor each enzyme and substrate combination: PDE1A (FAM cGMP) 70 nM,rhesus PD2A3 (FAM cAMP) 10,000 nM, PDE3A (FAM cAMP) 50 nM, PDE4A1A (FAMcAMP) 1500 nM, PDE5A1 (FAM cGMP) 400 nM, PDE6C (FAM cGMP) 700 nM, PDE7A(FAM cAMP) 150 nM, PDE8A1 (FAM cAMP) 50 nM, PDE10A2 (FAM cAMP) 150 nM,PDE11A4 (FAM cAMP) 1000 nM. The intrinsic PDE10 inhibitory activity of acompound which may be used in accordance with the present invention maybe determined by these assays.

The compounds of the following examples had activity in inhibiting thehuman PDE9 enzyme in the aforementioned assays, generally with a Ki ofless than about 1 μM. Many of compounds within the present invention hadactivity in inhibiting the human PDE9 enzyme in the aforementionedassays, generally with a Ki of less than about 0.1 μM. Additional dataare provided in the following Examples. Such a result is indicative ofthe intrinsic activity of the compounds in use as inhibitors of the PDE9enzyme. In general, one of ordinary skill in the art would appreciatethat a substance is considered to effectively inhibit PDE9 activity ifit has a Ki of less than or about M, where more potent inhibitors have aKi of less than or about 0. μM. The present invention also includescompounds within the scope of the invention which possess activity asinhibitors of other phosphodiesterase enzymes.

The subject compounds may be further useful in a method for theprevention, treatment, control, amelioration, or reduction of risk ofthe diseases, disorders and conditions noted herein. The subjectcompounds may be further useful in a method for the prevention,treatment, control, amelioration, or reduction of risk of theaforementioned diseases, disorders and conditions in combination withother agents. The compounds of the present invention may be used incombination with one or more other drugs in the treatment, prevention,control, amelioration, or reduction of risk of diseases or conditionsfor which compounds of the present invention or the other drugs may haveutility, where the combination of the drugs together are safer or moreeffective than either drug alone. Such other drug(s) may beadministered, by a route and in an amount commonly used therefore,contemporaneously or sequentially with a compound of the presentinvention. When a compound of the present invention is usedcontemporaneously with one or more other drugs, a pharmaceuticalcomposition in unit dosage form containing such other drugs and thecompound of the present invention may be desirable. However, thecombination therapy may also include therapies in which the compound ofthe present invention and one or more other drugs are administered ondifferent overlapping schedules. It is also contemplated that when usedin combination with one or more other active ingredients, the compoundsof the present invention and the other active ingredients may be used inlower doses than when each is used singly. Accordingly, thepharmaceutical compositions of the present invention include those thatcontain one or more other active ingredients, in addition to a compoundof the present invention. The above combinations include combinations ofa compound of the present invention not only with one other activecompound, but also with two or more other active compounds. Likewise,compounds of the present invention may be used in combination with otherdrugs that are used in the prevention, treatment, control, amelioration,or reduction of risk of the diseases or conditions for which compoundsof the present invention are useful. Such other drugs may beadministered, by a route and in an amount commonly used therefore,contemporaneously or sequentially with a compound of the presentinvention. Accordingly, the pharmaceutical compositions of the presentinvention include those that also contain one or more other activeingredients, in addition to a compound of the present invention. Theweight ratio of the compound of the present invention to the secondactive ingredient may be varied and will depend upon the effective doseof each ingredient. Generally, an effective dose of each will be used.Thus, for example, when a compound of the present invention is combinedwith another agent, the weight ratio of the compound of the presentinvention to the other agent will generally range from about 1000:1 toabout 1:1000, such as about 200:1 to about 1:200. Combinations of acompound of the present invention and other active ingredients willgenerally also be within the aforementioned range, but in each case, aneffective dose of each active ingredient should be used.

In such combinations the compound of the present invention and otheractive agents may be administered separately or in conjunction. Inaddition, the administration of one element may be prior to, concurrentto, or subsequent to the administration of other agent(s).

Accordingly, the subject compounds may be used alone or in combinationwith other agents which are known to be beneficial in the subjectindications or other drugs that affect receptors or enzymes that eitherincrease the efficacy, safety, convenience, or reduce unwanted sideeffects or toxicity of the compounds of the present invention. Thesubject compound and the other agent may be co-administered, either inconcomitant therapy or in a fixed combination.

In one embodiment, the subject compound may be employed in combinationwith anti-Alzheimer's agents, beta-secretase inhibitors, gamma-secretaseinhibitors, HMG-CoA reductase inhibitors, NSAID's including ibuprofen,vitamin E, and anti-amyloid antibodies.

In another embodiment, the subject compound may be employed incombination with sedatives, hypnotics, anxiolytics, antipsychotics,antianxiety agents, cyclopyrrolones, imidazopyridines,pyrazolopyrimidines, minor tranquilizers, melatonin agonists andantagonists, melatonergic agents, benzodiazepines, barbiturates, 5HT-2antagonists, and the like, such as: adinazolam, allobarbital, alonimid,alprazolam, amisulpride, amitriptyline, amobarbital, amoxapine,aripiprazole, atypical antipsychotics, bentazepam, benzoctamine,brotizolam, bupropion, busprione, butabarbital, butalbital, capuride,carbocloral, chloral betaine, chloral hydrate, clomipramine, clonazepam,cloperidone, clorazepate, chlordiazepoxide, clorethate, chlorpromazine,clozapine, cyprazepam, desipramine, dexclamol, diazepam,dichloralphenazone, divalproex, diphenhydramine, doxepin, estazolam,ethchlorvynol, etomidate, fenobam, flunitrazepam, flupentixol,fluphenazine, flurazepam, fluvoxamine, fluoxetine, fosazepam,glutethimide, halazepam, haloperidol, hydroxyzine, imipramine, lithium,lorazepam, lormetazepam, maprotiline, mecloqualone, melatonin,mephobarbital, meprobamate, methaqualone, midaflur, midazolam,nefazodone, nisobamate, nitrazepam, nortriptyline, olanzapine, oxazepam,paraldehyde, paroxetine, pentobarbital, perlapine, perphenazine,phenelzine, phenobarbital, prazepam, promethazine, propofol,protriptyline, quazepam, quetiapine, reclazepam, risperidone,roletamide, secobarbital, sertraline, suproclone, temazepam,thioridazine, thiothixene, tracazolate, tranylcypromaine, trazodone,triazolam, trepipam, tricetamide, triclofos, trifluoperazine,trimetozine, trimipramine, uldazepam, venlafaxine, zaleplon,ziprasidone, zolazepam, zolpidem, and salts thereof, and combinationsthereof, and the like, or the subject compound may be administered inconjunction with the use of physical methods such as with light therapyor electrical stimulation.

In another embodiment, the subject compound may be employed incombination with levodopa (with or without a selective extracerebraldecarboxylase inhibitor such as carbidopa or benserazide),anticholinergics such as biperiden (optionally as its hydrochloride orlactate salt) and trihexyphenidyl (benzhexol) hydrochloride, COMTinhibitors such as entacapone, MOA-B inhibitors, antioxidants, A2aadenosine receptor antagonists, cholinergic agonists, NMDA receptorantagonists, serotonin receptor antagonists and dopamine receptoragonists such as alentemol, bromocriptine, fenoldopam, lisuride,naxagolide, pergolide and pramipexole. It will be appreciated that thedopamine agonist may be in the form of a pharmaceutically acceptablesalt, for example, alentemol hydrobromide, bromocriptine mesylate,fenoldopam mesylate, naxagolide hydrochloride and pergolide mesylate.Lisuride and pramipexol are commonly used in a non-salt form.

In another embodiment, the subject compound may be employed incombination with a compound from the phenothiazine, thioxanthene,heterocyclic dibenzazepine, butyrophenone, diphenylbutylpiperidine andindolone classes of neuroleptic agent. Suitable examples ofphenothiazines include chlorpromazine, mesoridazine, thioridazine,acetophenazine, fluphenazine, perphenazine and trifluoperazine. Suitableexamples of thioxanthenes include chlorprothixene and thiothixene. Anexample of a dibenzazepine is clozapine. An example of a butyrophenoneis haloperidol. An example of a diphenylbutylpiperidine is pimozide. Anexample of an indolone is molindolone. Other neuroleptic agents includeloxapine, sulpiride and risperidone. It will be appreciated that theneuroleptic agents when used in combination with the subject compoundmay be in the form of a pharmaceutically acceptable salt, for example,chlorpromazine hydrochloride, mesoridazine besylate, thioridazinehydrochloride, acetophenazine maleate, fluphenazine hydrochloride,flurphenazine enathate, fluphenazine decanoate, trifluoperazinehydrochloride, thiothixene hydrochloride, haloperidol decanoate,loxapine succinate and molindone hydrochloride. Perphenazine,chlorprothixene, clozapine, haloperidol, pimozide and risperidone arecommonly used in a non-salt form. Thus, the subject compound may beemployed in combination with acetophenazine, alentemol, aripiprazole,amisulpride, benzhexol, bromocriptine, biperiden, chlorpromazine,chlorprothixene, clozapine, diazepam, fenoldopam, fluphenazine,haloperidol, levodopa, levodopa with benserazide, levodopa withcarbidopa, lisuride, loxapine, mesoridazine, molindolone, naxagolide,olanzapine, pergolide, perphenazine, pimozide, pramipexole, quetiapine,risperidone, sulpiride, tetrabenazine, trihexyphenidyl, thioridazine,thiothixene, trifluoperazine or ziprasidone.

In another embodiment, the subject compound may be employed incombination with an anti-depressant or anti-anxiety agent, includingnorepinephrine reuptake inhibitors (including tertiary amine tricyclicsand secondary amine tricyclics), selective serotonin reuptake inhibitors(SSRIs), monoamine oxidase inhibitors (MAOIs), reversible inhibitors ofmonoamine oxidase (RIMAs), serotonin and noradrenaline reuptakeinhibitors (SNRIs), corticotropin releasing factor (CRF) antagonists,α-adrenoreceptor antagonists, neurokinin-1 receptor antagonists,atypical anti-depressants, benzodiazepines, 5-HT_(1A) agonists orantagonists, especially 5-HT_(1A) partial agonists, and corticotropinreleasing factor (CRF) antagonists. Specific agents include:amitriptyline, clomipramine, doxepin, imipramine and trimipramine;amoxapine, desipramine, maprotiline, nortriptyline and protriptyline;fluoxetine, fluvoxamine, paroxetine and sertraline; isocarboxazid,phenelzine, tranylcypromine and selegiline; moclobemide: venlafaxine;duloxetine; aprepitant; bupropion, lithium, nefazodone, trazodone andviloxazine; alprazolam, chlordiazepoxide, clonazepam, chlorazepate,diazepam, halazepam, lorazepam, oxazepam and prazepam; buspirone,flesinoxan, gepirone and ipsapirone, and pharmaceutically acceptablesalts thereof.

The compounds of the present invention may be administered by oral,parenteral (e.g., intramuscular, intraperitoneal, intravenous, ICV,intracisternal injection or infusion, subcutaneous injection, orimplant), by inhalation spray, nasal, vaginal, rectal, sublingual, ortopical routes of administration and may be formulated, alone ortogether, in suitable dosage unit formulations containing conventionalnon-toxic pharmaceutically acceptable carriers, adjuvants and vehiclesappropriate for each route of administration. In addition to thetreatment of warm-blooded animals such as mice, rats, horses, cattle,sheep, dogs, cats, monkeys, etc., the compounds of the invention areeffective for use in humans. The terms “administration of” and or“administering a” compound should be understood to mean providing acompound of the invention or a prodrug of a compound of the invention tothe individual in need of treatment.

The term “composition” as used herein is intended to encompass a productcomprising specified ingredients in predetermined amounts orproportions, as well as any product which results, directly orindirectly, from combination of the specified ingredients in thespecified amounts. Such term in relation to pharmaceutical composition,is intended to encompass a product comprising the active ingredient(s),and the inert ingredient(s) that make up the carrier, as well as anyproduct which results, directly or indirectly, from combination,complexation or aggregation of any two or more of the ingredients, orfrom dissociation of one or more of the ingredients, or from other typesof reactions or interactions of one or more of the ingredients. Ingeneral, pharmaceutical compositions are prepared by uniformly andintimately bringing the active ingredient into association with a liquidcarrier or a finely divided solid carrier or both, and then, ifnecessary, shaping the product into the desired formulation. In thepharmaceutical composition the active object compound is included in anamount sufficient to produce the desired effect upon the process orcondition of diseases. Accordingly, the pharmaceutical compositions ofthe present invention encompass any composition made by mixing acompound of the present invention and a pharmaceutically acceptablecarrier.

Pharmaceutical compositions intended for oral use may be preparedaccording to any method known to the art for the manufacture ofpharmaceutical compositions and such compositions may contain one ormore agents selected from the group consisting of sweetening agents,flavoring agents, coloring agents and preserving agents in order toprovide pharmaceutically elegant and palatable preparations. Tabletscontain the active ingredient in admixture with non-toxicpharmaceutically acceptable excipients that are suitable for themanufacture of tablets. The tablets may be uncoated or they may becoated by known techniques to delay disintegration and absorption in thegastrointestinal tract and thereby provide a sustained action over alonger period. Compositions for oral use may also be presented as hardgelatin capsules wherein the active ingredients are mixed with an inertsolid diluent, for example, calcium carbonate, calcium phosphate orkaolin, or as soft gelatin capsules wherein the active ingredient ismixed with water or an oil medium, for example peanut oil, liquidparaffin, or olive oil. Aqueous suspensions, oily suspensions,dispersible powders or granules, oil-in-water emulsions, and sterileinjectable aqueous or oleagenous suspension may be prepared by standardmethods known in the art. By “pharmaceutically acceptable” it is meantthe carrier, diluent or excipient must be compatible with the otheringredients of the formulation and not deleterious to the recipientthereof.

The subject compounds may be further useful in a method for theprevention, treatment, control, amelioration, or reduction of risk ofthe diseases, disorders and conditions noted herein. The dosage ofactive ingredient in the compositions of this invention may be varied,however, it is necessary that the amount of the active ingredient besuch that a suitable dosage form is obtained. The active ingredient maybe administered to patients (animals and human) in need of suchtreatment in dosages that will provide optimal pharmaceutical efficacy.The selected dosage depends upon the desired therapeutic effect, on theroute of administration, and on the duration of the treatment. The dosewill vary from patient to patient depending upon the nature and severityof disease, the patient's weight, special diets then being followed by apatient, concurrent medication, and other factors which those skilled inthe art will recognize. Generally, dosage levels of between 0.001 to 10mg/kg. of body weight daily are administered to the patient, e.g.,humans and elderly humans. The dosage range will generally be about 0.5mg to 1.0 g. per patient per day which may be administered in single ormultiple doses. In one embodiment, the dosage range will be about 0.5 mgto 500 mg per patient per day; in another embodiment about 0.5 mg to 200mg per patient per day; and in yet another embodiment about 5 mg to 50mg per patient per day. Pharmaceutical compositions of the presentinvention may be provided in a solid dosage formulation such ascomprising about 0.5 mg to 500 mg active ingredient, or comprising about1 mg to 250 mg active ingredient. The pharmaceutical composition may beprovided in a solid dosage formulation comprising about 1 mg, 5 mg, 10mg, 25 mg, 50 mg, 100 mg, 200 mg or 250 mg active ingredient. For oraladministration, the compositions may be provided in the form of tabletscontaining 1.0 to 1000 milligrams of the active ingredient, such as 1,5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 600, 750,800, 900, and 1000 milligrams of the active ingredient for thesymptomatic adjustment of the dosage to the patient to be treated. Thecompounds may be administered on a regimen of 1 to 4 times per day, suchas once or twice per day.

Several methods for preparing the compounds of this invention areillustrated in the following Schemes and Examples. Starting materialsand the requisite intermediates are in some cases commerciallyavailable, or can be prepared according to literature procedures or asillustrated herein. The compounds of this invention may be prepared byemploying reactions as shown in the following schemes, in addition toother standard manipulations that are known in the literature orexemplified in the experimental procedures. Substituent numbering asshown in the schemes does not necessarily correlate to that used in theclaims and often, for clarity, a single substituent is shown attached tothe compound where multiple substituents are allowed under thedefinitions hereinabove. Reactions used to generate the compounds ofthis invention are prepared by employing reactions as shown in theschemes and examples herein, in addition to other standard manipulationssuch as ester hydrolysis, cleavage of protecting groups, etc., as may beknown in the literature or exemplified in the experimental procedures.Starting materials are made according to procedures known in the art oras illustrated herein. The following abbreviations are used herein: Me:methyl; Et: ethyl; t-Bu: tert-butyl; Ar: aryl; Ph: phenyl; Bn: benzyl;Ac: acetyl; THF: tetrahydrofuran; Boc: tert-butyloxycarbonyl; DIPEA:N,N-diisopropylethylamine; DPPA: diphenylphosphorylazide; EDC:N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide; EtOAc: ethyl acetate;HOBt: hydroxybenzotriazole hydrate; TEA: triethylamine; DMF:N,N-dimethylformamide; rt: room temperature; HPLC: high performanceliquid chromatography; NMR: nuclear magnetic resonance; TLC: thin-layerchromatography.

The compounds of the present invention can be prepared in a variety offashions. In some cases the final product may be further modified, forexample, by manipulation of substituents. These manipulations mayinclude, but are not limited to, reduction, oxidation, alkylation,acylation, and hydrolysis reactions which are commonly known to thoseskilled in the art. In some cases the order of carrying out theforegoing reaction schemes may be varied to facilitate the reaction orto avoid unwanted reaction products. The following examples are providedso that the invention might be more fully understood. These examples areillustrative only and should not be construed as limiting the inventionin any way.

According to the general synthetic scheme 1 above, appropriatelysubstituted 2H-benzo[d][1,3]-oxazine-2,4(1H)-diones A-1 can be reactedwith ethyl 2-cyanoacetate A-2 to give4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carbonitrile A-3. Chlorination ofA-3 with a POCl₃ and PCl₅ mixture yields substituted2,4-dichloroquinoline-3-carbonitriles such as A-4. Selective acidhydrolysis of the 2-Cl with TFA in water produces key intermediate4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile A-5, which can thenundergo nucleophilic displacement by alcohols A-6 to give products ofgeneral structure A-7.

EXAMPLES

Example compounds of the present invention can be synthesized accordingto the schemes and procedures outlined below. Because the schemes are anillustration, the invention should not be construed as being limited bythe chemical reactions and conditions expressed. The preparation of thevarious starting materials used in the schemes is within the skill of aperson versed in the art. Absolute stereochemistry of separatestereoisomers in the examples and intermediates was not determinedunless stated otherwise in an example.

Example 1

4-(Cyclohexyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile2,4-dihydroxyguinoline-3-carbonitrile (1-3)

To a round bottom flask, 2H-3,1-benzoxazine-2,4(1H)-dione (Aldrich, 82g, 503 mmol) was added and dissolved in DMF (300 ml). Ethyl cyanoacetate1-2 (62.5 g, 533 mmol) was then added slowly and the reaction was heatedto 100° C. for 5 hours, at which point it was allowed to cool and pouredinto H₂O. The H₂O layer was acidified to pH 1 with 0.5M aqueous HCl, theprecipitated solid was filtered and dried to give2,4-dihydroxyquinoline-3-carbonitrile (1-3), HRMS (M+H)⁺:observed=187.1, calculated=187.1

2,4-dichloroquinoline-3-carbonitrile (1-4)

2H-3,1-benzoxazine-2,4(1H)-dione (1-3) (11.9 g, 63.8 mmol), POCl₃ (44.0g, 287 mmol) and POCl₅ (26.6 g, 128 mmol) were added to a round bottomedflask and stirred at 100° C. for 2 hours. Upon completion, the reactionmixture was allowed to cool and slowly poured over ice mixture whilestirring virgourly. The precipitate was filtered off to give a yellowishsolid of 2,4-dichloroquinoline-3-carbonitrile (1-4), HRMS (M+H)⁺:observed=224.0, calculated=224.058

4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-5)

In a round-bottomed flask, 2,4-dichloroquinoline-3-carbonitrile (1-4)(15 g, 67.2 mmol), was dissolved in 40 ml of a 4:1 mixture of TFA andH₂O. The reaction mixture was heated to 100° C. for 1 hour, then allowedto cool and poured into methanol. The precipitate was filtered off anddried to give 4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-4)HRMS (M+H)⁺: observed=205.1, calculated=205.6

4-(cyclohexyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-7)

To a microwave flask charged with DMF (0.3 ml), cyclohexanol (50 mg,0.499 mmol) was added, followed by NaH (20 mg 60% dispersion in mineraloil, 0.499 mmol), portionwise. The reaction mixture was stirred at r.t.for 1 hour then 4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-4,51.1 mg, 0.250 mmol) was added. The reaction was heated to 110° C. undermicrowave irradiation for 10 min, cooled, the solvent removed and thecrude residue was purified via reverse phase to give4-(cyclohexyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-7). ¹HNMR (500 MHz, DMSO-d₆): δ 12.1 (s, 1H); 7.91 (m, 1H); 7.68 (m, 1H);7.35-7.23 (m, 2H); 5.22 (m, 1H); 2.09 (m, 2H); 1.80-1.69 (m, 4H);1.59-1.25 (m, 4H). HRMS (M+H)⁺: observed=268.31, calculated=268.31.

The following compounds were prepared according to the general procedureprovided in the examples and procedures herein using known or preparedstarting materials, as described in the reaction schemes and examplesherein. The requisite starting materials are either prepared asdescribed in the intermediates section, commercially available, or maybe prepared from commercially available reagents using conventionalreactions well known in the art without undue experimentation.

TABLE 1 LRMS m/z Ex- (M + ample Structure Name H) 1-8

4-(cycloheptyl- oxy)-2-oxo-1,2- dihydro- quinoline-3- carbonitrileCalc.: 283.1 Found: 283.3 1-9

2-oxo-4- tetrahydropyran- 4-yloxy-1H- quinoline- 3-carbonitrile Calc.:271.1, Found: 271.2 1-10

2-oxo-4-(2- hydroxymethyl- 2-methyl-1- butyloxy)- 1H-quinoline-3-carbonitrile Calc.: 287.1, found 287.4 1-11

4-((3-allyl- oxetan-3-yl) methoxy)-2- oxo-1,2- dihydro- quinoline-3-carbonitrile Calc: 297.12, found 298.3

The following table shows representative data for the compounds of theExamples as PDE9 inhibitors as determined by the assays describedherein. In this table, the PDE9 K_(i) is a measure of the ability of thetest compound to inhibit the action of the PDE9 enzyme. Such results areindicative of the intrinsic activity of the compounds for use asinhibitors of the PDE9 enzyme.

TABLE 2 Example PDE9 IMAP Ki (nM) 1-7 50.3 1-8 29.0 1-9 134.7 1-10 182.41-11 87.8

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.

What is claimed is:
 1. A compound of the formula I, or apharmaceutically acceptable salt thereof:

wherein: R⁵ is selected from the group consisting of: (1) —C₁₋₆alkyl,which is unsubstituted or substituted with hydroxy, oxetane, or allyl,(2) -tetrahydropyranyl, and (3) —C₆₋₇cycloalkyl; with the proviso thatthe compound is other than:4-(cyclohexyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile.
 2. Thecompound of claim 1 wherein R⁵ is C₁₋₆alkyl, which is unsubstituted orsubstituted with hydroxy, oxetane, or allyl.
 3. The compound of claim 1wherein R⁵ is -tetrahydropyranyl.
 4. A compound which is selected fromthe group consisting of:4-(cycloheptyloxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile;2-oxo-4-tetrahydropyran-4-yloxy-1H-quinoline-3-carbonitrile;2-oxo-4-(2-hydroxymethyl-2-methyl-1-butyloxy)-1H-quinoline-3-carbonitrile;and4-((3-allyloxetan-3-yl)methoxy)-2-oxo-1,2-dihydroquinoline-3-carbonitrile;or a pharmaceutically acceptable salt thereof.
 5. A pharmaceuticalcomposition which comprises an inert carrier and a compound of claim 1or a pharmaceutically acceptable salt thereof.